Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
In some networks, multiple users can share the same carrier for wireless communications simultaneously. For example, in a GSM network, a carrier is specified by an Absolute Radio Frequency Channel Number (ARFCN), which may be 200 kHz wide. The 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 45.005, Radio Transmission and Reception, Release 12, describes ARFCN in detail, which is incorporated into this specification by reference. Adjacent-channel interference (ACI) can occur when two users are assigned adjacent channels (e.g., adjacent ARFCNs) and are receiving and/or transmitting at the same time utilizing the adjacent channels. For example, in a GSM transmission (radio transmission), the actual time domain symbol is such that most of its energy lie within plus or minus (+/−) 100 kHz of the carrier; however, the symbol can have an overall presence up to +/−400 kHz or even further. Although a mobile station (e.g., a cellular phone, a user equipment, wireless terminal, etc.) is designed not to violate a predefined spectral mask, actual interference levels in practice can still be undesirably high due to higher imbalance between the ARFCNs and fading under mobility conditions.
Spurs (or spurious signals) are a form of radio frequency interference that may take the form of narrow-band frequency signals. Spurs can interfere with the desired signal, directly or indirectly. In general, spurs are signals close to the carrier frequency and may interfere with the carrier. At a mobile station, spurs emanate mainly, but not limited to, from the local oscillator used for clocking and tuning purposes.